The invention relates to a method for testing the solidity of vertically anchored masts. Furthermore the invention relates in particular to a device suitable for carrying out this method.
In the U.S. Pat. No. 5,212,654 methods for a destruction-free testing of masts with regard to their remaining solidity are described in order to still determine the loading still possible on the mast before this could break. If it is determined that the remaining solidity and thus the life-expectancy to be expected are too small, the mast concerned must be exchanged.
With these known methods for example it is proceeded such that the mast above it anchoring is loaded with a fixed predetermined force which corresponds to the previously calculated allowable residual solidity. If the lateral deflection of the mast after the force has reached the predetermined value is ascertained to be excessively high, this is a criterion for damage to the mast and the necessary exchange.
One also arrives at a suitable result when a previously calculated deflection corresponding to the theoretical residual solidity is predetermined and then the mast is loaded with a force from the side which increases until the deflection is achieved. If the force measured at the end of the testing procedure is ascertained to be excessively small then an exchange of the mast is to be carried out since with a damage-free and less elastic mast the force for reaching the fixed deflection would be comparatively larger.
Finally in the previously mentioned patent there is yet suggested a testing method with which the mast is loaded with a continuously measured force and simultaneously the lateral mast deflection is measured in order from these values at the end of the testing procedure to compute the residual solidity of the mast
With this method no provisions are made for the case that a damaged mast with increasing loading forces and bending moments makes a transition from the region of elastic deformation into a plastic deformation, thus could even buckle or break without this being able to be previously recognized and the test being stoped by releasing the mast loading. Inasmuch as this is concerned for this case it is only foreseen to support the mast with a frame or with cables, chains or likewise or to secure the mast loosely to a crane so that on buckling or breakage of the mast no damage may arise.
Furthermore the mast is still secured below, above its anchoring with a lock-nut so that the mast or its anchoring is fixed in tile ground against shifting. This however has the result that in the testing of the mast only the mast part which is located freely above the anchoring or the ground may be included and no details are possible as to the question whether or possibly the other part of the mast could be damaged or whether the mast at all is sufficiently stable.
In EP 0 638 794 A1 there is described a method for testing the solidity and bending resistance of a vertically anchored mast with which the mast likewise is subjected to a variable bending moment in that it is loaded with a force introduced above its anchoring and increasing in the course of the testing procedure, the measured value and the course of the force being used to determine the solidity of the mast. The mentioned force as well as also the distance about which the mast is laterally deflected at a selected location on account of the bending moment are measured simultaneously with sensors.
A linear dependency of the measured distance on the introduced force is evaluated as information of a mast deflection lying in the region of elastic deformation, whilst the determining of a non-linear dependency of the values measured by the sensors are evaluated as information of a plastic deformation and/or for a non-stable anchoring of the mast which is then recognized as not having bending resistance or is not stable and the testing procedure is stopped by unloading the mast. Thus with this method no safety precautions are to be made for the case that is not to be exected, specifically that the mast with this testing step may buckle or break. Moreover the testing procedure is only broken off by unloading the mast when a predetermined nominal value of the bending momemnt is achieved in the elastic region of deformation, which means that the mast is sufficiently stable and has bending resistance and does not need to be exchanged for another.
With all previously mentioned methods it is not possible to determine whether the mast tested in each case, in spite of deformation lying in the elastic region until reaching the testing load, is damaged by a fracture or by a corrosion region possibly going through the mast, so that in the case of such damage one may possibly arrive at an erroneous evaluation of the remaining stability of the mast, since for example with the application of the method according to EP 0 638 794 A1 a linear course of the function f=F(S), wherein F is the introduced force and S the lateral deflection of the mast, or a changing bending angle of the mast may give the delusion that the mast is not damaged.
This problem is solved by the method described in the Utility Model DE 296 07 045 U in which by way of a force unit the mast above its anchoring in the same plane of testing is loaded from the side, after one another with a compression force and with a tensile force, thus with oppositely directed bending moments so that for both cases of loading there results two functions f.sub.x and f.sub.y and these can be processed in an evaluation unit and compared. Furthermore these functions are usefully displayed on a monitor and/or graphically represented with a printer for the simultaneous assessment or subsequent evaluation.
These functions with an assumed straight course particularly give much information inasmuch as they give information whether there is damage caused for example by a fracture in the mast and where this damage is located.
If both functions f.sub.x, f.sub.y have the same course and thus the same gradient, it may be concluded that in any case no damage of the mast in the vertical testing plane and in the mast region directly next to this plane will be present. If on the other hand the courses of the two functions f.sub.x, f.sub.y related to the same zero point diverge and thus have differing gradients then a mast damage may be concluded even when the characteristic curves obtained from the two functions run linearly or straight, since a mast for example damaged with a fracture even after a further development of the fracture with an increasing loading of the mast will continue to behave elastically and a fracture formation at the most would result in a small kink in the otherwise continued linearly running characteristic curve.
As has already been mentioned, from the two functions obtained in the same testing plane and from their courses also the location of the damage may be concluded. If specifically e.g. the function f.sub.x evaluated with the compression procedure has a larger gradient than the function f.sub.y determined with the tensile procedure, this would mean that the fracture is located on the side of the mast on which the tensile force is indroduced, since it is to be expected that the mast on account of the smaller spreading of a transversly running fracture, without this at the same time having to become larger, will behave more elastically than with a compression force introduced in the opposite direction with which oppositely lying fracture surfaces are pressed together and the mast with this loading direction will behave less elastically as one without a fracture formation. In this context the same applies when the fracture would run vertically or with a vertical component, in the mast. On account of further criteria for assessing a mast to be tested the solutions specified in the Utility Model DE 296 07 045.9U are referred to, from which the invention also proceeds and of which the invention makes use.
All previously dealt with methods have the common disadvantage that with them the condition that the mast or its anchoring with the respective loading cases may change its position in or on the ground may not be exactly taken into account. In any case it may happen that with the testing procedures it may for example arise that movements and a tilting shifting of the mast or its anchoring may occur on or in the ground and at the same time ground material is permanently displaced by the tilting of the mast or its anchoring, which of course would have an such effect on the course of the functions f that these would no longer give clear information on the stability of the mast as such.